What Causes Sudden Weight Gain, Bloating And Constipation?

I have put on about 7 pounds this week. I have not changed my diet much (added more fruit due to issue) or routine. However, I am constipated and extremely bloated. I have tried lots of fruit and vegetables, and I took a laxative tonight because I look 9 months pregnant. I am not getting any relief. I have noticed for the past month that my gas has been terrible. I chalked it up to my new meds for my migraine prevention. I also noticed my poop getting more reddish-brown. Sometimes it looked like there was red blood, but I wasn't for sure if it was just the pigment of the feces. What should I do?